>>28163966>>28163991Usually ebay; Amazon doesn't generally have the really old ones but you can get the recently produced ones there. I've also bought some in physical stores (esp. the Nintendo store in NYC because I used to live there), but yeah, mostly ebay.
Pic is the one I just ordered. I've bought from that seller before and their stuff is real and good. They ship fast too so I bet you will see another thread like this in a few days!